Need advice about discipline

[Donthaveaclueaboutanyofthis]

I have 2 children with a large age gap (11 year old and a 3 month old). Ever since the baby arrived the 11 year old has been deliberately doing things to cause arguments and friction. For example: he will take his pile of clean clothes and put them in the dirty wash basket with all the dirty clothes. He refuses to go to school around once a fortnight. He has stolen money from us (spent it on books, sweets, junk food and fizzy drinks despite us having a plentiful supply of food in the house). He is disrespectful and refuses to do anything we ask and openly states that if we try to impose any kind of punishment he will ring social services and tell them the baby isn't safe with us. The baby is absolutely safe with us and there would be no basis to his accusation.
He has caused us problems over the years but recent months have been much worse. It probably started when he started senior school (so before baby was born). He is however jealous of the baby and never seems satisfied with however much attention we give him. He doesn't have any friends and I have tried organising cinema trips etc for him and others in his school who he says he gets on with but nobody ever wants to go with him.
After the latest ridiculous confrontation (he stole from us again) I have stopped his pocket money and changed the wifi password. I don't know what else to do. Where am I going wrong?

[Donthaveaclueaboutanyofthis]

Congrats if you made it to the end